Such a satellite is typically in the form of a rectangular parellelipiped, on which a north face and a south face, an east face and a west face, an earth face and an anti-earth face are defined. The north, south, east and west faces are thus named to correspond to the cardinal points of the planet around which the satellite is placed. The earth face is the one facing towards the earth; the anti-earth face is the opposite face. These orientations can be somewhat skewed with respect to their definition in order to meet certain operational or positioning constraints.
A severe constraint on a satellite concerns the thermal control of the different constituent parts and the dissipation of the heat load generated by these different constituent parts. The heat must then be removed from the satellite into space by radiation, by means of radiators, in order to maintain the equipment within an acceptable temperature range. The efficiency of a radiator in terms of thermal rejection capacity thus increases the less it is subject to solar radiation, also known as insolation. A solution for minimizing the insolation of the radiators is to place the radiative surfaces, i.e. the useful area of the radiator for removing heat, parallel to the north and south faces of the satellite.
A radiator is generally presented in the form of a panel, one or both faces of which form the radiative surfaces. A heat-transfer fluid flows between the various items of equipment of the satellite where it is heated, and passes to the radiative surfaces where it is cooled. The radiator can be mounted directly on the north face or the south face of the satellite, i.e. the radiative surface of the radiator is merged with the north face, or the south face, of the satellite. In particular in the case of deployable radiators, the radiative surfaces are not merged with a face of the satellite. Fluid connection means are then put in place outside the satellite, between the satellite and the radiator.
However, the satellite in orbit around the earth remains within a plane known as the tilted orbit plane relative to the sun's rays, as a result of the tilt of the axis of rotation of the earth on itself. For a geostationary satellite, the orbit of the satellite is in an equatorial plane, the tilt of which relative to the ecliptic plane is therefore 23.5°. Depending on the season, the solar incidence on the radiators parallel to the north and south faces of the satellite will thus vary from −23.5° to +23.5°. These two maximum values are reached at the solstices, and pass through the value of 0° at the equinoxes. Consequently, even if the radiative surfaces are placed parallel to the north and south faces of the satellite, they still receive a non-negligible part of the solar radiation, diminishing the efficiency of the radiator despite the presence of thermal blankets reducing the solar absorptivity.
Another constraint on a satellite concerns the space requirement. The satellite contains various items of equipment and in particular antennas, the field of view of which must be clear, for example of plasma thrusters, generating jets capable of damaging the equipment close by, or of solar panels, the surface area exposed to the sun of which must be as large as possible. Moreover, these items of equipment must also be taken into account in the launch phase of the satellite, during which the satellite is installed in a launcher and must be compatible with the effective volume. Generally, the items of equipment are then folded, and subsequently deployed once the satellite is launched into orbit. It can thus be understood that the greater the space requirement of the satellite, the more difficult it is to place it in the launcher. The radiators add to the space requirement.
Thus, the design and positioning of a radiator on a satellite must take account of this double constraint: minimizing the solar radiation received by the radiator while still taking account of the space requirement on the satellite.
Several solutions have already been proposed in the past.
A first solution is described in document U.S. Pat. No. 6,669,147, describing a deployable radiator for a satellite, mounted by means of a hinge, the angle of which is tilted relative to the principal axes of the satellite. The radiator would then not obstruct the other items of equipment. It is specified that when the radiator is pivoted by a motor on one axis, then its insolation can be reduced, but the insolation can only be reduced to zero by pivoting it on two axes. A mechanism is therefore proposed making it possible to obtain two axes of rotation of the radiator, in which a first annular part houses a motor for pivoting an intermediate part about a first axis. The mechanism also comprises a second annular motor, housed in the intermediate part in order to pivot a third part about a second axis.
Document U.S. Pat. No. 7,874,520 also proposes a deployable radiator, hinged on the satellite on two universal-joint type connectors, such that the radiator can be pivoted about a first axis and about a second axis, tilted relative to the first axis.
These two solutions thus make it possible, by means of pivoting the radiator relative to two axes, to reduce or even eliminate the insolation of the radiative surface of the radiator.
However, these solutions have the drawback of being complex. They involve taking account of two independent degrees of freedom in rotation, such that the control mechanism(s) are formed of several parts in order to achieve the result, increasing the space requirement and the costs. Moreover, the solutions with two axes of the state of the art pose a problem as regards passing the fluid connections between the satellite and the radiative surfaces of the radiator, as the connections must follow the two degrees of freedom in rotation. The pipes also undergo severe stresses due to the movements that they must follow, which can accelerate their wear. Generally, solutions are therefore developed that are specific to the fluid connections, increasing the costs of the satellite.
There is a need for a new radiator for a satellite providing in particular a solution to the aforementioned drawbacks.